Background: Thyroid nodules are common and the principal method of diagnosis is fine-needle aspiration cytology (FNAC).
Methods: To determine the value of FNAC in the diagnosis of thyroid nodules, thyroid cytology of 253 patients with definitive histology after surgery was analyzed from 1992 to 2002. FNAC was correlated with histology and the sensitivity, specificity and likelihood ratios were calculated. The method of FNAC and number of non-diagnostic aspirates were noted. The frequency of thyroid cancer was investigated in male and females who presented with a solitary thyroid nodule.
Results: The overall sensitivity of FNAC detecting thyroid neoplasia was 55.0%, specificity 73.7% and accuracy 67.2%. Likelihood ratios indicate that a 'malignant' or 'suspicious for malignancy' cytology dramatically increase the pretest probability of thyroid neoplasia. There were no false positive 'malignant' FNAC. Ultrasound guided FNAC had a significantly lower non-diagnostic rate compared to freehand FNAC (P < 0.02). Of 22 males, 22.7% who proceeded to surgery for their solitary nodule had thyroid carcinoma compared with 11.9% of 167 females (P = 0.02).
Conclusions: FNAC was essential to management in this series of patients. 'Malignant' or 'suspicious for malignancy' cytology are absolute indicators for thyroidectomy. FNAC should be undertaken with ultrasound guidance and if possible with a pathologist in attendance to assess sample adequacy. We recommend a high index of suspicion of thyroid cancer in the male patient who presents with a solitary nodule. If solitary nodules are to be observed, repeat FNAC should be undertaken because of the high false negative rate.